1. Field of the Invention
The present invention relates to a double feed detecting device of sheet members and a method of controlling the double feed detecting device in a feeding device which mounts a plurality of sheet members thereon, and separates and feeds the sheet members one by one. In particular, the present invention relates to double feed detection in feeding the sheet members while the sheet members are enclosed in an envelope for a sheet member feed protection.
2. Description of the Related Art
As a conventional sheet member feeding device, there is provided a device which separates and feeds sheet members one by one, for example, in a scanner or a copying machine. There is a fear in that there occurs a double feed such as parts or all of two or more sheet members are fed while those sheet members are being overlapped with each other despite that only one sheet member should be fed. For that reason, a function for detecting the double feed is required for the sheet member feeding device. As the device for detecting the double feed of the sheet members, there has been become widespread an ultrasonic double feed detecting device for detecting an air spacer between overlapping papers by an aid of ultrasonic waves in the diverse fields, as disclosed in Japanese Patent Application Laid-Open No. 2004-231403.
FIG. 4 is a diagram showing an outline of a conventional ultrasonic double feed detecting device. In FIG. 4, a sheet member A01 to be fed is a paper in this example. An ultrasonic transmitting portion A02 transmits ultrasonic waves to a paper A01. An ultrasonic receiving portion A03 receives ultrasonic waves transmitted by the ultrasonic transmitting portion A02. Also, as shown in FIG. 4, the ultrasonic receiving portion A03 is so disposed as to face the ultrasonic transmitting portion A02 through a path of the paper A01 so as to receive the ultrasonic waves, which have been transmitted through the paper A01. A waveform analyzing portion A04 analyzes a receiving signal of the ultrasonic waves, which have been received by the ultrasonic receiving portion A03, and detects the double feed.
The double feed detecting device shown in FIG. 4 analyzes a change in an amplitude or a phase of the received ultrasonic waves through the waveform analyzing portion A04 to detect the double feed. A system which detects the double feed based on a change in the amplitude of the ultrasonic receiving signal is called “level determining system,” and a system which detects the double feed based on a change in the phase of the ultrasonic receiving signal is called “a phase determining system.”
The level determining system will be further described. The ultrasonic receiving portion A03 receives the amplitude of the ultrasonic waves, which have been transmitted through the paper A01 during feeding the paper A01. The amplitude of the ultrasonic receiving signal is small because attenuation of the ultrasonic waves is large in a case where the paper A01 is doubly fed as compared with the amplitude of the ultrasonic receiving signal in a case where the paper A01 is normally fed one by one. Accordingly, the amplitude of the ultrasonic waves which have been received by the ultrasonic receiving portion A03 is compared with a predetermined double feed determination threshold value in the waveform analyzing portion A04, thereby making it possible to detect the double feed of the paper A01 based on a comparison result.
The phase determining system will be further described. The phase information on the ultrasonic receiving signal which has been obtained by the ultrasonic receiving portion A03 is held a given period of time after a timing when the ultrasonic waves are transmitted from the ultrasonic transmitting portion A02. The phase information when no paper A01 exists between the ultrasonic transmitting portion A02 and the ultrasonic receiving portion A03 is set as basic phase information. The phase information during feeding the paper A01 is compared with the basic phase information, thereby making it possible to detect the double feed of the paper A01 based on comparison results.
As disclosed in Japanese Patent Application Laid-Open No. 2000-061407 or Japanese Patent Application Laid-Open No. H08-048439, there has been proposed an optical double feed detecting device which detects the overlapping sheet members by means of an optical sensor.
In the sheet member feeding device, there is a case where the sheet members are enclosed in a transparent or semi-transparent feed protection envelope, and then fed because of prevention of the sheet members from being damaged or a damaged sheet member, except that a normal sheet member is fed.
In the double feed detecting device using the ultrasonic waves in the sheet member feeding device as described in the description of the related art, it is impossible to discriminate a case where the sheet members are doubly fed and a case where the sheet members are enclosed in the envelope for the sheet member feed protection and then fed. For that reason, in the case where the sheet members are enclosed in the sheet member feed protection envelope and fed, the ultrasonic double feed detection must be nullified.
In the device for detecting the overlapping sheet members by means of the optical sensor, the transparent envelope cannot be detected.